In recent years, portable spas have become increasingly popular. However, conventional spas typically exhibit one or more of a number of problems. Most such units are composed of a synthetic insulating material covered by an external liner. These spas often do not exhibit the structural integrity, rigidity and durability that is desired for extended use of the unit. Additionally, conventional spa units usually exhibit an insufficient water circulation capacity because the number of jets are limited by the piping that is used. Indeed, in one known spa, shown in Popovich, U.S. Pat. No. 4,981,543, the circulating pipe for the unit extends outside of the tub and the circulating pump is contained in a separate and distinct housing. This unit employs only one pair of jets, which provide very limited circulation and hydrotherapy for bathers. Due to the small number of jets used, heating of the water may take an undesirably long time and such heating may be uneven. Moreover, the unit is undesirably bulky and difficult to transport and store. It also exhibits the lack of rigidity and structural integrity described above.